1. Field of the Invention
The present invention relates generally to systems for assembling a printed circuit board by mounting a set of components or parts on a substrate (including a ceramic substrate), and more particularly to a system most suitable for assembling printed circuit boards, like those for a large-scale computer, in flexible manufacturing that requires a large number of complicated manufacturing stations.
2. Description of the Related Art
Heretofore it has been a common practice to use printed circuit boards for main circuits in computers, electronic equipments of control systems, and the like. For production of the individual printed circuit board of computers, for example, a CPU, memories, various interfaces, a controller, etc. are fabricated into LSI circuits, and then several kinds of such LSI circuits, along with other electronic components such as resistors, are packaged into a single unit at high density.
Usually, these kinds of printed circuit boards are required to be manufactured efficiently within a short period of time to reduce production time and also to minimize the production costs. Also it is required to accurately mount necessary parts on a substrate accurately.
In a conventional system, for assembling 100 kinds of printed circuit boards on a single parts mounting apparatus using 20 kinds of parts in all, for example, the parts mounting apparatus is equipped with a parts supply unit which is capable of supplying any of 20 kinds of the parts optionally so that any intended printed circuit board, of 100 kinds of printed circuit boards, can be assembled. This conventional system is exemplified by Japanese Utility Model Laid-Open Publication No. 72898/1986.
FIG. 3 is a fragmentary perspective view illustrating the manner that the parts are supplied to a parts mounting area in the parts mounting apparatus of the conventional system. Although in the conventional system, 20 kinds of parts are supplied, only three kinds of parts are illustrated in FIG. 3 for clarity. Also the parts mounting apparatus is omitted in FIG. 3 for clarity.
In FIG. 3, parts 72 are commercially available parts such as TTLs (Transistor Transistor Logic circuits); three kinds of TTLs named A, B and C, for example, are carried to the vicinity of a substrate 74 by three conveyors 81, 82, 83, respectively.
To mount the TTLs named A on the substrate 74, the part 72 is taken out from the forward end of the conveyor 81 and is then attached in a predetermined position of the substrate 74. Then the conveyor 81 is moved an amount corresponding to a single part, whereupon the next part 72, like the preceding part, is taken out from the conveyor 81 and is then attached in another predetermined position on the substrate 74. This procedure is repeated until an intended number of parts have been attached to their predetermined positions on the substrate 74.
Upon completion of mounting of all the parts, the substrate 74 of FIG. 3 is discharged to a subsequent station, and then the next substrate (generally, different from the preceding substrate in number of parts to be mounted and also in mounting positions) is supplied to the parts mounting area.
In the example of FIG. 3, the foregoing procedure is repeated to assemble 100 kinds of printed circuit boards using the three kinds of parts in total.
Therefore, to mount 20 kinds of parts in total on 100 kinds of substrates, for example, 20 conveyors are provided for supplying the 20 kinds of parts to the parts mounting station where the parts are to be mounted on the corresponding substrate.
However, with this prior arrangement, if the number of kinds of parts to be mounted on 100 kinds of substrates increases up to 10,000 kinds of parts in total, it requires 10,000 conveyors provided adjacent to the parts mounting station for supplying 10,000 kinds of parts thereto. Consequently, a gigantic, complicated parts supply apparatus would be necessary, although various countermeasures are possible.
Besides, the cost of fabricating such a huge supply apparatus is considerable and is at variance with the reality; yet real conditions cannot pliably cope with the increase and change of the kinds of parts.
The conventional system requires not only a warehouse to store therein many kinds of parts taken in by manufacturing or purchasing, but also an apparatus for taking out necessary parts from the warehouse and then placing them on the corresponding conveyors. Like the supply apparatus, either the warehouse or the apparatus still have to be complex and large-sized in order to comply with every kind of parts.
Further, the conventional system does not intend to encompass the bringing-in and storing of parts and substrates needed for assembling printed circuit boards and the preparing of the substrates as well as encompass progressing status of the assembling. Since it cannot have a real-time understanding of these facts, any possible unnecessary stop cannot be determined with ease when assembling a wide variety of kinds of printed circuit boards. As a consequence, a streamlined production is difficult to achieve, and the individual printed circuit board is difficult to manufacture in a short period of time.
In the meantime, control systems, such as factory control systems and production control systems, using a computer have recently been developed. For example, an automatic machine is located along the parts conveying line and is controlled by a computer.
However, any one of the prior control systems aims at a centralized control of the working automatic machine and conveying line, which does not necessarily meet the reality. Especially when mounting many kinds of parts, each kind in a small quantity, (e.g., 10,000 kinds of parts, each kind including only a single part) on many kinds of substrates (e.g., 100 kinds of substrates), the prior control system should preferably have carried out assembling so as to take measures suited to the situation, i.e. status of the parts and substrates on the site.
In addition, it is laborious and time-consuming to input to a computer the progressing status of manufacture of many kinds of parts and substrates. In this connection, it is possible to recognize the individual articles using bar codes. If many kinds of articles were recognized individually at every station, it would take considerable time to perform data inquiry and data transfer processing, increasing the latency of each automatic machine.